Definitely no cotton balls with infants OR toddlers. Yup, total choking hazard. Try making some pom poms instead. They're super easy to make and you can pack them up and reuse them another time. We did a 'Winter Woollies' theme for a month in my daycare. For 1 week, I had multi coloured pom poms I'd made in the sensory bin. Then a week with cheap wool hats and 2 weeks with cheap/old mittens and gloves. It was great!!! The Dollar Store will carry those items which can be used year to year. Get hats, mitts with different knits for the changes in texture, appearance and weight. In the fall we did gourds, which was very popular. Brushes are good as well...soft bristled baby brush, make up brushes, paint brush, nail brush. If you're feeling really ambitious, you could make little 'pillows' of different scents of potpourri, teas, etc. Make sure they're double or triple lined to avoid tears and little bits coming out. Smelly sensory bins are fun! Plus, you can change up the fabrics to add in tactile changes.

There are a few ideas I've used that have worked well.